Frequency compensated saturable reactor system



May 30, 1950 s. E. HEDSTRGM ET AL 2,509,855

FREQUENCY COMPENSATED SATURABLE REACTOR SYSTEM Filed Aug. 16, 1947 9. 4. 1 //1 yen fars 51/01 t'r/c f/a/sfra/u A; F0602 fr /7x50 Patented May 30, 1950 FREQUENCY COMPENSATED SATURABLE REACTOR SYSTEM 1 Sven Eric Hedstriim and Robert Svensson, Ludvika, Sweden, assignors to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application August 16, 1947, Serial No. 769,027 In Sweden August 19, 1946 In a known connection of regulators operating with direct current saturable reactors, in which the regulated quantity consists of or is represented by a voltage, the reactor is provided with two direct current windings opposing each other, which are connected to the said voltage across two impedances having essentially different characteristics so that the windings will mutually compensateeach others action for a certain normal voltage, while the influence of one or the other winding predominates as soon as the voltage exceeds or falls below the said normal voltage. As a rule, it is most convenient, especially if the regulated or representative voltage is an alternating current voltage, to construct the impedances essentially as reactances and rectify the traversing currents. In this case it is, as a rule, most appropriate to construct one of the reactances with a practically straight characteristic and the other with a characteristic strongly differing from the straight form. The most simple way of obtaining such a characteristic is to employ an inductance with a normally saturated iron core, but sometimes a more complicated type is employed for instance an inductance of the aforesaid kind in parallel with a capacity, which after rectifying the current gives an 8- shaped characteristic, of which the portion utilized for the regulation has a negative value of the derivative of the current with respect to the voltage. Hereby a more accurate voltage regulation can be obtained under otherwise equal conditions.

An inconvenience of the use of two such reactances having strongly different characteristics is, however, that the position of the point of intersection and thereby the value of the regulated quantity will depend rather strongly on the frequency. The present invention relates to a device for avoiding this inconvenience, which is essentially characterized by the fact that the impedance having the most nearly straight characteristic. is composed in such manner of an impedance and a capacity that the slope of its characteristic will be essentially more dependent on the frequency than that of the characteristic of a simple inductance. In which direction the slope should be altered upon an alteration of the frequency depends on the characteristic of the other inductance, as is made clear by the followmg.

A form of the invention is diagrammatically illustrated in Fig. '1 of the accompanying'drawing, where Fig. 2 shows a diagram of the manner of operation of this form and Fig. 3 a corresponding diagram for a somewhat different form. P18.

8 Claims. (Cl. 323- 89) 4 shows a portion of a modified form 01 the in vention.

In Fig. 1, the numeral 2 designates an inductance with a normally saturated iron core, which is connected in series with a rectifier 3 between a pair of alternating current terminals i, the voltage between which is to be re ated. On the direct current side, the rectifier 3 is connected to a winding 4 of a direct current saturable reactor having an alternating current winding 5. 6 designates an essentially constant impedance, which is connected in parallel with a condenser 1 between the voltage terminals l and a rectifier 8, which feeds a winding 9 of the same reactor 5. The winding 9 opposes the winding 4. Load I0 is connected in the alternating current circuit in series with winding 5.

The current through the winding 4 as a function of the voltage between the terminals l is represented at normal frequency by the curve A in Fig. 2, where the abscissae designate currents and the ordinates voltages. The current through the winding 9 is similarly represented by the straight line B. The windings 4 and 9 should have the same number of turns so that the curves A and B also represent their numbers of ampereturns. When these are equal at the point of intersection e, the regulator should be in equilibrium, and it thus tends to maintain the voltage corresponding to the point e. If the frequency now rises by for instance 20%, the curve A is replaced by the dotted curve A1 provided that the inductance 2 essentially determines the current in the winding 4, If a constant impedance (for instance an ohmic resistance) were connected in series with the winding 9, the new point of intersection would be the point a corresponding to a voltage raised by more than 20%. If a simple frequency-dependent impedance, for instance an inductance without a normally saturated iron core, were connected in series with the winding 9, the line B would be changed into the line B1,

which intersects the curve A1 in the point :21,

which lies 20% above the point e and thus gives a voltage raised by 20%. By a suitable mutual dimensioning of the constant inductance 6 and the condenser I; it is, however, possible to make the line B change into the line B2, which intersects the curve A1 in the point as, which is at the same level as the point eand thus gives the same voltage at the increased frequency. With the form illustrated of the curve A and the dimensions 11- lustrated, this corresponds, as a calculation shows, to a value of the admittance of the condenser, which at normal frequency is about 0.38

d of that 01' the inductance, and generally it should be smaller than the admittance of the inductance, i. e. the value of the inductance should be smaller than that giving resonance with the capacity at norma1 frequency.

Instead of keeping the regulated voltage entirely constant during frequency variations as just described, it may in certain cases be advisable to cause the said voltage to vary slightly with a varying frequency, either in the same direction as the frequency or in the opposite direction. An alteration of the frequency is generally caused by an alteration of the proportion between the supply and demand of electric power, and this proportion may sometimes be influenced by a voltage regulation. Such a mall variation of the voltage with the frequency can easily be accomplished by a suitable proportioning of the admittances of the inductance t and the condenser i.

If in Fig. l, in a manner lmown per se, a condenser is connected in parallel to the inductance 2, the characteristic A in Fig. 2 can be modified to the form shown by the curve C in Fig. 3. The point of intersection f between this curve and the straight characteristic D represents in this case the normal value of the voltage. When the frequency is raised by the curve C is changed into 01, and the point of intersection f1 between this curve and the line D1, rotated in proportion to the increase of frequency, represents an essentially raised voltage. For restoring in this 'case the normal voltage value, a rotation of the line D in the opposite direction is necessary, namely to the position D2, which obviously depends on the fact that the derivative of the voltage with respect to the current of the curve C is negative within the region in question. A rotation to the position D2 can be obtained in a parallel connection of an inductance and a condenser by makins the admittance of the latter greater than that of the former.

The increased sensibility to the frequency of the substantially constant impedance may also be obtained by composing the said impedance of an inductance t and a condenser l in series as shown in Fig. i, which is otherwise similar to Fig. 1. A calculation in this case shows that a value of the ratio between voltage and current, which increases with the frequency, such as is necessary in Fig. 2, is obtained, if the reactance of the inductance at normal frequency is greater than the numerical value of the reactance of the condenser, while a value of the said ratio, which decreases upon an increase of frequency, as necessary according to Fig. 3, is obtained if the reactance of the inductance at normal frequency is lower than the numerical value of the reactance of the condenser.

We claim as our invention:

1. An electric regulator comprising an alterhating current voltage source normally operating at a certain frequency, a direct current saturable reactor influencing said voltage source to keep its voltage normally constant, a first circuit fed by said alternating current voltage source and containing a highly voltage dependent impedance, a rectifier, and a saturating winding of said reactor, a second circuit fed by said alterating current voltage source, containing a capacity and another substantially constant impedance considerably out of resonance with said capacity, a rectifier, and a saturating winding of said reactor opposing the aforesaid saturating winding, the mutual dimensioning of said capacaccuses ity and said constant impedance being such as to reduce the influence of frequency variations upon the resultant saturating ampereturns of said saturable reactor.

2. An electric regulator comprising an alternating current voltage source normally operating at a certain frequency, a direct current saturable reactor influencing said voltage source to keep its voltage normally constant, a first circuit fed by said alternating current voltage source and containing a highly voltage dependent impedance 3. An electric regulator comprising an alternating current voltage source normally operating at a certain frequency, a direct current saturable reactor influencing said voltage source to keep its voltage normally constant, a first circuit fed by said alternating current voltage source and containing a highly voltage dependent indepedance giving, in the neighborhood of normal voltage, a negative value of the derivative of the voltage with respect to the current, said first'circuit containing further a rectifier and a saturating winding of said reactor, a second circuit fed by said alternating current voltage source and containing in parallel a capacity and a substantially constant inductance larger than that giving resonance with said capacity at normal frequency, said second circuit containing further a rectifier and a saturating winding of said reactor opposing said first-named saturating winding.

4. An electric regulator comprising an alternating current voltage source normally operating at a certain frequency, a direct current saturable reactor influencing said voltage source to keep its voltage normally constant, a first circuit fed by said alternating current voltage source and containing a highly voltage dependent impedance giving, in the neighborhood of normal voltage, a positive value of the derivative of the voltage with respect to the current, said first circuit containing further a rectifier and a saturating winding of said reactor, a second circuit fed by said alternating current voltage source and containing in series a capacity and a substantially constant inductance larger than that giving resonance with said capacity at normal frequency, said second circuit containing further a rectifier and a saturating winding of said reactor oppos ing said first-named saturating winding.

5. An electric regulator comprising an alternating current voltage source normally operating at a certain frequency, a direct current saturable reactor influencing said voltage source to keep its voltage normally constant, a first circuit fed by said alternating current voltage source and containing a highly voltage dependent impedance giving, in the neighborhood of normal voltage, a negative value of the derivative of the voltage with respect to the current, said first circuit containing further a rectifier and a saturating winding of said reactor, a second circuit fed by said alternating current voltage source and containing in series a capacity and a substantially constant inductance smaller than that giving resonance with said capacity at normal frequency, said second circuit containing further a rectifier and a saturating winding of said reactor opposing said first-named saturating winding.

6. An electric regulator comprising an alternating current voltage source, a saturable reactor, a first circuit fed by said voltage source and containing a highly voltage dependent impendance, a rectifier and a saturating winding of said reactor, and another circuit fed by said voltage source containing a capacity, another substantially constant impedance considerably out of resonance with said capacity, a rectifier, and a saturating winding of said reactor opposing said first named saturating winding.

7. An electric regulator comprising an alternating current voltage source normally operating at a certain frequency, a direct current saturable reactor influencing said voltage source to keep its voltage normally constant, a first circuit fed by said alternating current voltage source and containing a highly voltage-dependent impedance and a saturating winding of said reactor, a second circuit red by the alternating current voltage and containing a combination of a capacity and a substantially constant reactor in dissonance at normal frequency and so dimensioned with respect to each other that the phase angle diflerence between the voltage impressed 'on said combination and the resultant current flowing therethrough has the same sign as the derivative of the voltage with respect to the current of said voltage-dependent impedance in the neighborhood of normal voltage, said second circuit containing further a rectifier and a saturating winding on said direct current saturable reactor, opposing said first-named saturating winding.

8. An electric regulator comprising an alter- 40 nating current voltage source normally operating at a certain frequency, a direct current saturable reactor influencing said voltage source to keep its voltage normally constant, a first circuit fed by said alternating current voltage source and containing a highly voltage-dependent impedance and a saturating winding of said reactor, a second circuit fed by the alternating current voltage and containing a capacity and a substantially constant reactor in such a connection that characteristic quantities of the group reactance and admittance thereof are added together, the

diflference between the numerical values of that REFERENCES CITED The following references are of record in the file of this patent:

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